For various reasons, it may be desired to maintain a drop laid on a surface, accurately centered on a predetermined axis. A known way (by the inventor) consists of modifying around this axis the surface wettability with respect to the drop liquid.
FIG. 1 shows a side cross-section view of a liquid drop 2 laid on a surface 4. Surface 4 has been processed in a circular area C1 centered on an axis O. The processing of area C1 is such that its wettability with respect to the liquid of drop 2 is strong. Thus, capillarity forces maintain drop 2 centered on axis O.
An improvement, not shown, of such a surface processing consists of creating around axis O several concentric circular areas. The processing of these areas then is such that the closer an area is to axis O, the more its wettability with respect to the liquid of drop 2 is strong. Such an improvement enables centering drop 2 for different contact angles. This is particularly advantageous when a way of changing said angle is available, for example by means of an electric voltage. Such surface processings may however be difficult and expensive to implement.
An object of the present invention is to center a drop laid on a surface without using a modification of the surface wetability.